#1 Learn All the Details of the Events
The old saying, "the devil is in the details", would be better put in this case as "the devil is in the details you FORGET". Knowing the most intricate parts of your event will ensure that your event planning doesn't leave any important factors out and moves smoothly from start to finish.
For example, knowing that your guests have food allergies, that your guests need a close location to commute to, or that you require a venue that offers ample parking or a handicap ramp. Having specific details pertaining to your event well thought out and listed in advance will prevent situations from turning into a catastrophe in your event planning.